This invention relates to a device for interconnecting the socket of an artificial lower limb to the skeletal portion of the prosthesis. In particular, it relates to a torque absorbing device which permits limited rotational movement of the socket relative the skeletal portion.
Prosthetic lower limbs have progressed from rather crude exoskeletal devices to the present relatively sophisticated endoskeletal devices having a cosmetic outer surface closely approximating, at least visually, a normal human leg. In addition to the improvement of the structure of the prosthesis, development has progressed at the same pace in the necessary hardware to construct such an artificial prosthesis. The difficulties in the design and construction of such hardward are compounded in that the weight of the various elements must always be closely controlled while retaining the strength and the versatility of the various elements.
One unique problem encountered in a lower limb prosthesis is the rotational movement imparted to the prosthesis by the amputee swinging the stump with the subtending prosthesis in a para-saggital plane during walking. This rotational movement of the prosthesis is caused by the swinging of the hip of the amputee in order to walk. For example, as a leg is swung forward to take a step, the one hip swings forward relative the other hip. In view of the face that the entire pelvis is rotating about a vertical axis through the center of the hips and generally coincident with the line of intersection of the frontal plane and the saggital plane, a prosthesis subtending from a hip would also rotate about the same axis. When a prosthetic foot affixed to the prosthesis contacts the ground, the hip may be rotated 10-15.degree. out of the frontal plane. As the amputee then lifts the other foot and swings the other leg forward, the other side of the hip will swing relatively forward, while the one side moves relatively backwardly. With no rotational capability of a prosthesis, the one prosthetic foot, which may have been placed on the ground in a relatively unnatural position, will remain in that unnatural position and may become more unnatural throughout the step with the other foot off the ground. If this were to be accepted, the stump of the amputee would rotate in the socket of the prosthesis. In addition to the awkwardness imparted to the walk, the forced rotation could prove to be discomforting to the amputee over an extended period of time.
Therefore, it has been found appropriate to include, at least in the endoskeletal type prosthesis, means to allow rotation of the prosthesis relative the socket. It is necessary, however, to install some sort of a resilient return means in such arrangements. In addition to the resiliency which must be imparted to the rotational device, means have to be provided in the device to permit mounting of the socket to the endoskeletal portion of the prosthesis. Commonly, this has been accomplished by a relatively large flat plate member made, in some cases, of wood to save weight. The flat plate member is then molded into the socket or screwed thereto by appropriate fastening means. In some cases the torque absorber or "rotator" as it is also called is positioned at the ankle thereby increasing the moment of the swinging leg to an almost unacceptable level.
It was with this problem in mind that the present invention was developed. Specifically, the problem of weight, compounded by the rather large plate member in the existing torque absorber joints which also may impart a high moment due to poor placement, and the resiliency requirement resulted in the present invention.